1. Field of the Invention
The present invention relates generally to the field of surface testing instruments, and more particularly relates to the field of surface testing instruments for performing scratch, mar, and wear-resistance testing on material samples.
2. Background of the Invention
Surface testing and analysis of materials, particularly of polymers, is becoming a rapidly expanding area of research in the field of materials science and mechanics. The surge of interest in the subject of scratch and/or mar resistance of polymers stems from the increasing use of polymers in various applications such as in hard discs, optical lenses, windshields, automotive parts, durable goods, etc.
In general, there are two basic types of material surface damage—mar and scratch. A mar is a mark caused by a sliding body that is too shallow to be perceived by the casual human eyes alone but nevertheless may become visible when present in large quantities. Examples of mar include the typical damage found on paint coats and dashboard surfaces damaged by small pointed objects such as rough stones, sticks, keys etc. A scratch is a mark that forms visible grooves and/or surface damage, often referred to as “whitening” of the scratched surface. A scratch is the typical damage mode for surfaces that withstand heavier moving loads. “Whitening” of the scratched surface is a key damage mechanism that has prompted much concern in industries and applications where surface aestheticism or residual strength of the scratched/marred article may be important.
By using a scratch testing device, scratches and/or mars may be made on the surface of a material sample. Analysis of the scratch and/or mar during and after the scratch test may provide useful data and insight into the material properties or surface characteristics of the samples tested. Further, a better understanding of the micromechanical properties of materials, derived from surface testing and analysis, and a better understanding of the mechanical process of surface damage may enable quantitative evaluation in the scratch and/or mar behaviors of various materials under a variety of conditions. For example, scratch tests may indicate the critical load at which whitening occurs at the surface of a given material, or scratch tests may aid in predicting the ability of a given material to withstand scratch and mar surface damage.
Currently, there are limited means and methods recognized for surface testing and analysis. Further, most conventional surface testing devices and methods have some drawbacks. For instance, conventional testing means may yield inconsistent and irreproducible data and results. For example, the stylus of some conventional testing devices may “skip” or “jump” during testing, thereby contributing to inconsistent testing results. Inconsistent and irreproducible data and results may not allow a true comparison between different samples and tests. In addition, the range of loads that can be applied during scratch testing and the range of scratch speeds may be limited in most conventional and commercial devices. Further, conventional devices may not allow for variable load or variable scratch speed testing in a single test. Still further, some conventional scratch testing devices may be unable to measure and capture quantitative data (e.g., load, scratch speed, scratch depth, etc.) during the actual surface test. Many conventional devices merely provide a scratched and/or marred sample for separate study, which is generally qualitative. Without gathering quantitative data during testing, it may not be possible to verify that the intended load conditions and scratch speed actually occurred during testing.
Consequently, there is a need for improved apparatus and methods for surface testing and analysis. In addition, there is a need for surface testing devices and methods which produce reliable and consistent results. Further, needs include improved surface testing apparatus and methods that provide the ability to carry out multi-pass, load-controlled scratch tests with variable scratch speed. Still further, needs include improved surface testing apparatus and methods that measure and capture critical quantitative data (e.g., loads, scratch speed, scratch depth, etc.) during surface testing.